Twenty-five-year-old mixed martial artist Sergio Salcido Luna and 28-year-old Kevin Joel Romero were shot and killed early Monday morning when attempting to enter the United States from Mexico at a border crossing near San Diego, according to a Fox News report.

The two were waiting at the San Ysidro border crossing on the Tijuana side when an unidentified suspect with a 9-mm handgun fired off five shots, reportedly hitting the two men in the head, chest, and arms.

Surveillance cameras were unable to pick up a clear view of the attacker, who remains at large.

Law enforcement officials told Fox News that neither Luna nor Romero had a criminal record, and they did not yet know the motive for the attack.

Luna fought under the name Sergio Salcido, primarily for Gladiator Challenge and other California based fight promotions. He had a professional record of 4-5 at the time of his death.

Fellow fighter and sometime training partner Evan Anthony characterized Salcido as a “really tough fighter, old school type fighter” in an interview with Fox 5, KSWB in San Diego.